Transverse magnetic devices providing controllable variable inductance and mutual inductance



Oct. 10, 1961 D M. LIPKIN 3 0 TRANSVERSE MAGNETIC DEVICES PROVIDINGCONTROLLABLE VARIABLE INDUCTANC'E AND MUTUAL INDUCTANCE Filed March 17,1955 Max. Loss Region Of lncreaslngly Effective Clamping Action BetweenB And H Vectors FIG. I.

E G mmtm Applied Field Oersteds l fl hp Asymptotic FIG. 2.

lad lml 1 R)? Choke S ecandary Primary D. C. Bias 0 C. 36 las l-lLongitudinal INVENTOR. DANIEL M. LIPKIN l I I 394 4 Modulated R F.

Output 8 Longitudinal Linear Induction FIG. 3.

l Auxiliar C 2 Bios A Larger Value of Bias One Particular Value of BiasSignal Input B: H H

A GENT United States Patent Ofifice 3,004,171 Patented Oct. 10, 19613,004,171 TRANSVERSE MAGNETIC DEVICES PROVIDING CONTROLLABLE VARIABLEINDUCTANCE AND MUTUAL INDUCTANCE I Daniel M. Lipkin, Philadelphia, Pa.,assignor to Sperry Rand Corporation, a corporation of Delaware FiledMar. 17, 1955, Ser. No. 494,946

7 Claims. (Cl. 307-88) The present invention concerns radio-frequencytransformers employing transverse magnetization and having vanishinglysmall core losses.

It is an object of the invention to provide a substantially loss-lesscontrollablevariable reaotance or modulator.

It is an object of the invention to provide a controllable variablereactance or modulator having a core of magnetic material which is to beoperated in a magnetic field of higher value than that required tosaturate the magnetic material comprising the core. a

It is an object of the invention to provide a radio-ire quencytransformer having a core of magnetic material With a substantiallyrectangular characteristic loop to be operated in a magnetic fieldgreater than that required for saturation.

It is a particular purpose of the present invention to provide loss-lesstransverse magnetic circuit components which exhibit variable selfinductance and variable mutual inductance. In these devices a biascurrent is varied to produce controllable variation, and it has beenfound that the mutual inductance depends inversely upon the magnitude ofthe bias current, whereby the device can be used as a variableself-inductor, variable mutual inductor, or modulator. Loss-lessoperation can be a particularly desirable factor in designs employingthese components.

Among the magneticmatcrials that may be used in this invention are thosehaving a substantially rectangular hysteresis characteristic. Copendingapplication Serial No. 494,903 for Transverse Magnetic Amplifier, ofeven date herewith, is referred to for background discussion of thepresent invention which supplements the present disclosure. 7

The basic considerations concerning transverse devices comprising thepresent invention may be formulated as follows:

(1) Transverse fields are in general applied to a core of ferromagneticmaterial simultaneously. It may be noted that the BH relationships arequantitatively unknown except under the conditions to be describedbelow.

(2) It is possible by means of the invention to obtain quantitativelypredictable B-,-H relationships in trans verse core structures,consisting in the resultant B vector being a simple mathematicalfunction of the resultant H vector.

(3) The above is accomplished by observing strictly the condition thatthe scalar magnitude of the vector resultant magnetizing force be keptabove a predeterminable level characteristic of the magnetic material.

(A) When the above condition is met, the vector flux density B issubstantially given by the vector equation: (1) B I? where Bs is thesaturation flux density magnitude for the material; H is the resultantmagnetizing force vector in g the material; and h is the scalarmagnitude of H. The

(E) When Equation l is satisfied, the core itself does P where hp is thepredeterminable level referred to in 3 above 1 (5) In a practicalembodiment, a transverse magnetic structure, constructed in accordancewith the foregoing considerations, would comprise a body of magneticmaterial having magnetizing means associated therewith and adapted toimpress mutually orthogonal fields on the said body. An output etfectmay be produced from such a transverse structure by varying themagnitude of at least one of the transverse fields and, so long as thecondition represented by Equation 2 is satisfied, the operation of thedevice will be substantially loss-less.

(6) The predeterminable level hp referred to above, may be taken to bethat value of magnetizing field larger than the value at which thespecific rotational hysteresis loss for the material peaks (seeFIGURE 1) and for which the specific rotational hysteresis loss isappreciably less than said maximum rotational hysteresis loss.

In the drawings, like numerals refer to like parts throughout.

'FIGURE 1 is a loss diagram for a ferromagnetic core.

FIGURE 2 is a schematic diagram of a controllable variable reactanceaccording to the invention having unregion of vanishing rotationalhysteresis loss is reached and any changes of magnetization of the corewill take place without storage'or irreversible loss of energy in thecore or shell. Just Where the region of substantially diminishingrotational loss occurs will vary greatly as the characteristichysteresis loop departs from a rectangle which gives the steepest slopefor the curve of FIGURE 1. This curve is not necessarily symmetrical,but starts nearthe origin, passes through a more or less criticalmaximum and is asymptotic to the X axis as field H increases. The regionweare here concerned with lies to the right of this maximum. 5

In the region beyond the maximum rotational loss, an increase in appliedfield tends to bring the magnetic field closer to saturation. Under'acondition of saturation, the field and flux vectors have substantiallythe same direction, and as the field vector rotates, the flux vectortends to rotate with it continuing in the same direction as the fieldvector. At lesser values of the field, the field and flux vectors havedifferent directions and the angle between them may vary. Thischaracteristic of the saturated fiux vector having the same direction asthe field vector is termed clamping action between the flux and fieldvectors B and H in FIG. 1' and elsewhere in this specification andincertain claims.

In FIGURE 2, a core of magnetic material 20 is made in the form of along slender cylinder having a central channel .21 therethrough.Threading the channel 21 is a winding 22 having two radio-frequencychokes 23 and 24 as part of its circuit. Winding 22 is provided withterminals 25 for connection to a bias current supply. Around thecylinder 22 is wound a radio-frequency input winding 26 provided withinput signal terminals 27. A second winding 28, spaced from winding 26,is also wound around core 20 and provided with terminals 29. Winding 28is a radio-frequency output winding and may be regarded as a secondary,while winding 26 may be regarded as a primary winding.

The material of tube 29 is preferably ferro-magnetic and coils 23 and 2are quite large so as to inhibit severely A.C. current flow in thecircuit of winding 22. Although winding 22 is shown as a single turn, itmay, of course, be any number of turns that the design of the device mayindicate as desirable.

The structure of FIGURE 2 can be used as a controllable mutual inductoror as a modulator by varying the applied currents. If current wereapplied to coil 22 only, the produced magnetic flux would becircumferential and would not induce a potential in the secondary 28.The concurrent application of a signal to the primary 26, however,causes the resultant magnetic flux vector to deviate from a strictlycircumferential direction and to attain a longitudinal component. It isthis deflection or rotation of the resultant flux vector which effectsinduction of a voltage in the secondary. Without this deflection towardthe longitudinal axis of core 20, there could not be any mutualinductance between windings 26 and 28. Since the degree of deflectiondepends on the relative values of the currents in coils Z2 and 26, avariation of the current flowing through coil 22 will vary the inductivecoupling between the primary and the secondary, modulating anyelectrical waveform which may be transferred from the primary to thesecondary and, thus, affecting the latters output at terminals 2 9. TheBH relationship for coil 26 (assuming coil 28 to be open), if it weremeasured without knowledge of the transverse bias current in coil 22,would be the following:

Jfi Bius where Bs is the saturation induction for the core material,HBias is the transverse magnetizing field due to the bias current incoil 22; and in the usual sense: H is the longitudinal magnetizing fielddue to current in coil 26 and B is the component of induction linkingcoils 26 and 28 (i.e. longitudinal component of induction in FIG. 2).

The following facts should be noted:

(1) The BH relationship is expressible analytically, provided that H Ehpat all times.

(2) The BH relationship is free of hysteresis.

(3) The BH relationship is such that coil 26 acts as a hysteresis-freesaturable reactor, with saturation induction Bs.

(4) FIGURE 4 shows in its center a dotted square representing a regionof substantially linear induction where H is smaller than HBias onaccount of relatively small currents in coil 26. In this region coil 26acts as a linear inductor. It is, thus, apparent that the linearinductance of coil 26 depends inversely on the value of H The way inwhich H influences the BH relationship for coil 26 is indicated by thetwo curves in FIGURE 4. The solid curve shows the effect of a relativelysmaller H while the dotted curve illustrates the efiect of acomparatively larger H This provides the basis for a hysteresis-freecontrollable mutual inductor and a modulator the operation of which iscontrolled through selection of values of the HBi (5) Assuming now thatcoil 28 is energized. If and when the combined magnetic field of bothcoils 26 and 28, due to the currents in these coils, is less inmagnitude than H then each coil acts as a linear self-inductor, and bothcoils possess a linear mutual inductive coupling. Furthermore, all threeinductance values, the two selfinductances and the mutual inductance,are influenced inversely by the value of the HBias while bearingconstant proportions to one another.

- In FIGURE 3 a magnetic modulator or amplifier utilizing transversemagnetization comprises a long slender ferromagnetic tube 30* having acentral channel 31 through which are threaded a signal input winding 32supplied with terminals 31, and a bias current winding 33 having largeradio-frequency choke coils 34 and 35 in its circuit. Windings 33 aresupplied with terminals 36 for connection to a bias supply. Around thecircumference of tube 38 is wound an auxiliary radio-frequency winding37 having terminals 38 for connection to an auxiliary radio-frequencycurrent source. A second Winding 39, also around core 35} but spacedfrom winding 37, is provided with terminals 4% from which may be taken amodulated radio-frequency output signal. This device employs theprinciple of design discussed above in connection with FIGURE 2, but hasa signal current augmenting the action of the bias current. The sheet ofthis combination is to change the mutual inductance between theauxiliary and output windings 37 and 39 and therefore the magnitude ofthe output voltage at terminals 40. The output may then be detected bysuitable rectification.

The circuit of FIGURE 3 has the advantage that the induced highfrequency voltage appearing across the signal winding 32 has at leasttwice the frequency of current flowing in the auxiliary radio-frequencywinding 37. With this difference in frequency, it is relatively easy toeliminate such induced voltages in the signal winding 32. by includingtuned traps or the like in its circuit.

The structure of FIGURE 3 may be used as a modulator. Modulation iseffected by virtue of a signal input applied to terminals 31 adding toor detracting from the bias current in winding 33 and, thereby, varyingthe magnitude of the net bias field.

While there have been described above what are presently believed to bepreferred forms of the invention, the appended claims are intended toinclude all variations thereof which fall within the true spirit of theinvention.

I claim:

1. A magnetic device comprising a saturable magnetic element, aplurality of winding means linked to said element and respectivelyassociated with transverse directions of magnetization, means forenergizing at least a part of each of said winding means simultaneouslyand at least one of said parts in a varying amount with the netmagnetizing force produced by said winding means when energized beingsufficient to maintain said element in substantial saturation, and meansfor deriving output signals from a part of one of said winding means.

2. A magnetic device comprising a saturable magnetic element, aplurality of windings linked to said element and arranged to applymagnetizing forces thereto in a plurality of transverse directions,means for energizing said windings and at least one thereof in a varyingamount with the net magnetizing force produced by said windings duringoperation being sufficient to maintain said element in substantialsaturation, and an output winding linked to said element.

3.'A magnetic device as recited in claim 2 wherein said output Windingis linked transversely to said one winding that is to be energized in avarying amount.

4. In combination, a device comprising a ferro-magnetic core, a firstWinding on said core comprising means to supply a first current to saidfirst winding, a second winding on said core comprising means to supplya variable current thereto simultaneously with said first means, a thirdwinding on said core comprising signal input means whereby a suppliedsignal can be modulated and a fourth winding on said core comprisingmodulated signal output means whereby a modulated signal output may beobtained.

' 5. The combination set forth in claim 4, means for controlling thevalue of at least one of said first and second means to supply current.

6. The combination set forth in claim 5, said first current being directcurrent and said first winding having choke means connected thereto.

7. The combination set forth in claim 4, said first winding and saidsignal input winding being so positioned on said core that their fieldscombine to vary the net bias 1,794,717 Lindenblad Mar. 3, 1931 fieldprolcluced thereby? h fi f th- OTHER REFERENCES eferences cued m l e 1e0 18 Patent Abstract of application S.N. 212,266, published June UNITEDSTATES PATENTS 5 30 1953 (L do f) 1,208,982 Hartley Dec. 17, 1918

